1. Field of the Invention
The present invention relates to a laminate packaging flat cell enhancing the stability of a thermally welded portion. More specifically, the present invention relates to a laminate packaging flat cell ensuring the stability of an electrode terminal lead and a laminate film in the thermally welded portion by providing a through-hole in the electrode terminal lead of the thermally welded portion, and further relates to a battery module and an assembled battery which are formed of the cells.
2. Description of the Related Art
Recently, air pollution caused by exhaust gas from vehicles has become a global problem. In such a context, electric vehicles, which use electric power as a motive power source, and hybrid cars, which are run by a combination of an engine and a motor, have been attracting attention. Correspondingly, the development of a cell having a high energy density and a high output density to be mounted on these hybrid cars has an important place industrially. As a configuration of a cell for such use, there is a configuration in which a wound electric power generating element is housed within a cylindrical case. In another configuration, a wound electric power generating element or an electric power generating element, which stacks planar electrodes and a separator, is housed within a flat case.
Since these cylindrical or flat cases are required to have enhanced strength, it is necessary to form these cases as metal cans. Therefore, there is a problem in that the reduction of weight is difficult. Thus, as a means of reducing the weight of the cell as well as obtaining a higher energy density and a higher output density, the prior art as described in Japanese Patent Application Laid-Open No. 11-224652 (1999) is cited. In this conventional technology, a structure of the cell using a laminate film as an outer case, a periphery of which is sealed by thermal welding to close the outer case hermetically, has been proposed.
In the cell as described above, which uses the laminate film as the outer case, the sealing capability thereof is sometimes damaged due to a deformation caused by an external force and an increase of an internal pressure caused by a temperature rise of the cell. Particularly, when the cell is mounted on the electric vehicle or the hybrid car, the cell temperature sometimes rises to approximately 60° C. In this case, a large current flows through an electric terminal lead during charge/discharge, and therefore, the temperature of the electrode terminal lead sometimes becomes higher than the cell temperature by approximately 30° C. Hence, the temperature of the electrode terminal lead sometimes reaches a softening point (approximately 90° C.) of resin in the laminate film. In such a situation, the sealing capability of a region where the resin in the laminate film and the electrode terminal lead contact each other is damaged in some cases due to the increase of the cell's internal pressure caused by the rise of the internal temperature thereof. Therefore, in the cell as described above, which uses the laminate film as the outer case, ensuring a sealing capability equivalent to a metal case or more has become an important subject. Accordingly, as a technology of coping with such a request, an attempt has been made, which is to enhance the sealing capability by providing a coating layer formed of olefin resin containing a titanate coupling agent in a position corresponding to the thermally welded portion of the electrode terminal lead. In this case, the olefin resin is also used for an adhesive layer and the innermost layer of the laminate film (refer to Japanese Patent Application Laid-Open No. 2000-133218).